build up lines are lines that are made up from vacations and training and odd pairings that dont fit into a line. they can be high hour lines or goofy, crappy lines. Hard to tell. They do let you "request" things like weekends off, but ultimately you are at the mercy of crew scheduling. As a junior guy, you will get whatever dregs are left over.

No matter where you are in the system, routes will get routine (if not boring). Just remember, this is a job. Even wh#res get tired of scr$wing.